The increasing user acceptance as well as technological progress in the development of new broad band servicesxe2x80x94also referred to as multimedia servicesxe2x80x94lead to an increasing need for broad band transmission sources in communication networks that already exist or are to be newly installed. In order to effectively and economically realize broad band applications, particularly multimedia services making use of high data transmission ratesxe2x80x94for example, xe2x80x9cvideo on demandxe2x80x9d, video conference, toy shopping or telebankingxe2x80x94, a broad band communication network, particularly a broad band offering network is required. In currently installed offering networks, the network resources available are divided onto the network termination units connected to the communication network or onto the communication terminal devices connected to the network termination units. The access of the network termination units or of the communication terminal devices to the commonly used transmission mediumxe2x80x94for example, light waveguides or radial channelxe2x80x94is thereby controlled such by a transmission method that respectively only one network termination unit or communication terminal device is at least temporarily granted the access authorization.
Given an offering network realized by wireless radio channels, a plurality of network termination unitsxe2x80x94also referred to as network terminationsxe2x80x94are connected to a base station centrally arranged in a radial cellxe2x80x94also referred to as radial base station. The data transmission ratexe2x80x94for example, an aggregate bit rate of 155 Mbit/sxe2x80x94available in the offering network is thereby divided onto the network termination units currently connected to the base station. In current wireless offering networks, different transmission methods respectively adapted to the required data transmission rates are utilized for the data to be transmitted in the direction of the network termination unitsxe2x80x94also referred to as the downstream directionxe2x80x94and for the data to be transmitted from the network termination units to the base stationxe2x80x94also referred to as the upstream direction. Time-division multiplex or time-division multiple access methodxe2x80x94also referred to as TDMA methodxe2x80x94represents one transmission method utilized for the data to be transmitted in the upstream direction or the data streams to be transmitted. In this transmission method, brief signal sequencesxe2x80x94also referred to as signal burstsxe2x80x94are sent to the base station in alternation by the network termination units. Access onto the transmission medium or onto the radial channel is controlled by the base station such that respectively only the network termination unit sends information or, respectively, a signal burst to the base station.
In existing offering networks with light waveguide transmission, for example in a SOAP systemxe2x80x94Siemens Optical Advanced PONxe2x80x94a signal burst covering 60 bytes of digitized data or, respectively, a data frame covering 60 bytes of dataxe2x80x94also referred to below as SOAP data framexe2x80x94is transmitted in the upstream direction by a respective termination unit. The preamble of each SOAP data frame comprises 7 bytes, or by 40 bits of the preamble covering 7 bytes are provided as synchronization bits for the determination of the signal parameters of the signal bursts arriving at the receiver side. The determination of the signal parameters, i.e. the determination of the amplitude as well as of the carry and clock phase within the time available for the synchronizationxe2x80x9440 bits herexe2x80x94is also referred to as xe2x80x9cRuninxe2x80x9d. Different wireless offering networks comprising radial channels, the data to be communicated from the network termination units to the base station, i.e. the SOAP data frame to be transmitted, is advantageously modulated onto a carrier signal at a predetermined frequency with a coherent modulation method, usually by a phase modulation method that is also referred to as Phase Shift Keying PSK. Offset quadrature four phase keyingxe2x80x94also referred to as Offset-Quadrature-Phase-Shift-Keying OQPSKxe2x80x94has proven to be an advantageous modulation method for the transmission of digitally existing data via radial channels. Since the individual network termination units respectfully sending a signal burst at different points in time have different distances from the base station, the amplitude as well as the carrier and clock phase during the xe2x80x9cRuninxe2x80x9d must be respectively identified for each signal burst arriving at the base station. Only a very brief time interval of 258 ns during the xe2x80x9cRuninxe2x80x9dxe2x80x94corresponding to the time duration of the transmission of the 40 synchronization bits of the SOAP data framexe2x80x94are thus available for the realization of a radial system having an aggregate bit rate of, for example, 155 Mbit/s for determining the signal parameters of signal bursts arriving at the base station. In particular, the carrier phase of the carrier signal transmitted burst-like must be very exactly identified for an optimum demodulation of the data transmitted via a radial channel and a synchronization must be produced for the demodulation.
U.S. Pat. No. 4,095,187 discloses a demodulator for phase-modulated carrier signals wherein an incoming, first, analog, phase-modulated carrier signal is synchronized with a second analog carrier signal generated with the assistance of a voltage-controlled oscillator allocated to the demodulator. The phase-modulated carrier signal incoming at the demodulator is demodulated and, dependent on the demodulation result, the second carrier signal locally generated in the demodulator is modulated or xe2x80x9cre-modulatedxe2x80x9d. The phase of the incoming, phase-modulated carrier signal is compared to the phase of the re-modulated carrier signal with the assistance of a phase comparator and the voltage-controlled oscillator is driven dependent on the comparison result.
Further, U.S. Pat. No. 4,757,272 discloses a demodulator for regeneration of an analog reference carrier signal and for demodulation of a phase-modulated, four-phase PSK modulation signal that is transmitted burst-like. The four-phase PSK modulation signal transmitted burst-like comprises a preamble, whereby the preamble is at least partially modulated with a predetermined modulation symbol at the transmission side. For reception-side generation of the reference carrier signal, the received four-phase PSK modulation signal is modulated with the predetermined modulation symbol during the reception of the preamble, i.e. is inversely modulated, whereby a regenerated, analog carrier signal without phase-modulated parts is formed. The regenerated carrier signal is subsequently supplied to what are referred to as AFC means that, among other things, realize a PLL circuit arrangement. With the assistance of the AFC means, the frequency-corrected and phase-corrected reference carrier signal is derived from the regenerated carrier signal, this being subsequently forwarded to an orthogonal demodulator for demodulation of the incoming four-phase PSK modulation signal.
The present invention is based on the object of improving the synchronization for the demodulation of information or data modulated onto a carrier signal transmitted burst-like.
This object is achieved in accordance with the present invention in a method for fast synchronization of a first analog carrier signal generated at a transmitter with a second carrier signal generated in a receiver, said method comprising the steps of: at least partially modulating a preamble of said first carrier signal with a predetermined phase position at said transmitter; modulating said second carrier signal with said same predetermined phase position at said receiver; identifying a phase difference between said modulated first carrier signal and said modulated second carrier signal; and following a phase difference recognition time, correcting a phase position of said second carrier signal by said identified phase difference.
This object is also achieved in accordance with the present invention in an arrangement for fast synchronization of a first analog-carrier signal generated in a transmitter with a second carrier signal generated in a receiver. A transmitter has a first modulator for an at least partial modulation of a preamble of the first carrier signal with a predetermined phase position. A receiver has a second modulator for modulation of the second carrier signal with the predetermined phase position, a phase difference identification device for determining a phase difference between a modulated first carrier signal and a modulated second carrier signal, and a correction device for correction of a phase position of the second carrier signal by an identified phase difference.
The critical aspect of the inventive method for fast synchronization of a first, analog carrier signal generated at the transmission side with a second carrier signal generated in a receiver is comprised therein that, at the transmission side, a preamble of the first carrier signal is at least partially modulated with a predetermined phase position and, at the reception side, the second reference carrier signal is modulated with the same, predetermined phase position. The phase difference of the modulated first carrier signal and of the modulated second carrier signal is subsequently identified, and, after a phase difference recognition time, the phase position of the second modulated reference carrier signal is corrected by the identified phase difference.
As a result of the inventive method, advantageously, the phase difference between the two modulated carrier signals is acquired very fast, i.e. within the xe2x80x9cRuninxe2x80x9d that covers only a very short time spanxe2x80x94also referred to as phase difference recognition time belowxe2x80x94and is thus identified, for example within a time span of 100 through 200 nmxe2x80x94whereby the phase position of the second carrier signal is very exactly adapted to the phase position of the first carrier signal following the phase difference recognition time. While existing, a digital reference carrier signal, is digitally modulated with the predetermined phase position and is subsequently converted from digital to analog. In an embodiment, the phase difference of the two modulated carrier signals is identified in analog fashion and, following the phase difference recognition time, the phase position of the second, modulated reference carrier signal is digitally corrected by the identified phase differencexe2x80x94claim 3. In an embodiment, given a digitally existing reference carrier signal, the first, analog carrier signal is converted analog-to-digital, and the phase difference of the two modulated and digitalized carrier signals is digitally determined. Following the phase difference recognition time, the phase position of the second, modulated reference carrier signal is digitally corrected by the identified phase difference. As a result of the advantageous, digital correction of the phase position of the second modulated reference carrier signal, disadvantages of analog methods for correction of a phase differencexe2x80x94for example, temperature and voltage drift, offset and balancing proceduresxe2x80x94are avoided and, thus, the quality of the demodulation of the message data communicated by the first carrier signal is improved.
In an embodiment, during the phase difference recognition time, advantageously, phase signals representing the phase difference are formed, whereby the values of the phase signals are stored at the end of the phase difference recognition time. Following the phase difference recognition time, the phase position of the second carrier signal is corrected by the phase difference represented by the stored values of the phase signals. As a result of the advantageous storing of the values of the phase signals, circuit-oriented and arrangement-caused transient responses during the phase difference recognition time are avoided or one waits for them to end, and, thus, precise acquired values of the phase difference are stored, as a result whereof potential errors in the correction of the phase position of the second carrier signal by the identified phase difference are minimized.
In an embodiment, a digital, modulated reference carrier signal is derived from the second carrier signal, whereby the digital, modulated carrier signal having the predetermined phase position is formed during the phase difference recognition time and, following the phase difference recognition time, the digital, modulated reference carrier signal is formed with the phase position corrected by the identified phase differencexe2x80x94. In an embodiment, during the phase difference recognition time, the digital, modulated second carrier signal is formed with the assistance of phase values representing the predetermined phase position and digital phase signals representing the phase difference. At the end of the phase difference recognition time, the phase values represented by the digital phase signals are stored and additional phase values are derived from the stored phase values and stored. After the phase difference recognition time, the digital, modulated second carrier signal is formed with the assistance of the stored values and of the stored, additional phase valuesxe2x80x94. As a result of this embodiment, i.e. due to the derivation or generation of digital signals, the disadvantages occurring in analog circuits or arrangementsxe2x80x94for example, temperature and voltage driftxe2x80x94are avoided and, thus, the quality of the demodulation of the message data transmitted by the first carrier signal is avoided.
In an embodiment, advantageously, the digital, modulated second carrier signal is converted digital-to-analog, and is converted into an analog, first sub-carrier signal having the first frequency. Further, an analog, second sub-carrier signal having a second frequency is derived from the second carrier signal. The modulated, second carrier signal having the predetermined phase position or the phase position corrected by the identified phase difference is formed from the first and second sub-carrier signal, whereby the modulated second carrier signal comprises a frequency exhibiting the sum of the frequencies of the first and second sub-carrier signalsxe2x80x94. As a result of this embodiment, digital means for deriving and generating said digital signals can be clocked with a low clock frequencyxe2x80x94for example, less than or equal to 155 MHzxe2x80x94and, thus, the inventive method can be realized in an especially economical fashion.
Another embodiment provides for fast synchronization of a first analog carrier signal having a predetermined phase position with a second reference carrier signal with the assistance of a digital unit. The digital unit is advantageously realized with a low number of simple, digital components, being realized in an extremely cost-beneficial way and with little technological outlay, whereby fast ASDICS or PGAs are available for the realization.